The present invention pertains to non-woven products of natural or synthetic fibers having good heat stability, good wet strength and a low amount of crosslinking agents such as urea-formaldehyde or N-methylolacrylamide.
Such non-woven webs include a large number of products from papers of natural or synthetic fibers to loose webs of cellulose or synthetic fibers including synthetic organic fibers such as rayon, polyesters, or nylon and synthetic inorganic fibers such as glass. Non-woven webs may be wet laid, carded or air laid. The fibers are bound together with a bonding agent which may be a naturally occurring binder such as starch or protein or a synthetic polymer.
There has been an increasing use of non-woven products in our society. Non-wovens of natural or synthetic organic fibers are used for wiping cloths, disposable table cloths, disposable clothing such as lab coats, diapers, surgical drapes and disposable bedding. In these applications there is a growing trend to reduce or eliminate crosslinking agents which may irritate the skin. Such crosslinking agents tend to enhance the wet tensile strength of the web when it is being impregnated with the binder. Non-wovens of inorganic fibers such as glass are used to produce webs which may be used to make shingles or road underlay material.
In the past one of the major synthetic binders for non-wovens has been acrylate latices. These latices contained polymers which have a low level of unsaturation and are more stable to heat and light degradation than binders containing conjugated diolefins. Acrylic binders tend to be relatively expensive and this contributes to the cost of the finished web. In some instances antioxidants when used may be incompatible with inks and dyes intended to be used on the web as the antioxidant may interfere with the curing of the ink. It would be desirable to find a low cost method of providing a non-woven web having good heat and light stability. The heat aging properties of the compounds of the present invention, particularly those based on carboxylated SBR latices, or vinyl acetate type latices suggest that such compounds could be utilized as low cost paints.
Typical of the current state of the art of non-woven webs are: U.S. Pat. No. 4,356,229 issued Oct. 26, 1982, assigned to Rohm and Haas Company; European patent application No. 0 071 932 published 16.02.83 in the name of the B. F. Goodrich Company; European patent application No. 0 012 032 published 11.06.78 in the name of Rohm and Haas Company; and U.S. Pat. No. 4,268,546 issued May 19, 1981, assigned to The Dow Chemical Company. These patents illustrate the current trend in the art to use acrylate polymers in manufacturing non-woven webs.
Much of the work done with the heat stability of polymers has been based on polyvinyl chloride. A very good discussion of the current state of technology of heat stabilizers appears in Chapters 8 and 9 of Encyclopedia of PVC, Vol. 1, edited by Leonard I. Nass, Marcel Dekker Inc. 1976. This text shows at page 298 that sodium and potassium oxides or hydroxides are not considered heat and light stabilizers.
British patent specification No. 848,808 teaches the use of latex in manufacturing paper. The British patent discloses that the latex may be neutralized with a fixed alkali such as NaOH subsequent to polymerization. The patent teaches that during the curing operation the alkali ion must be replaced with a polyvalent ion to crosslink the polymer. This is not required nor desirable in the present case.